Radioactive material such as fissile fuel elements used in nuclear reactors for the generation of steam in nuclear electric power plants are commonly stored upright in racks. The fuel elements are arranged and spaced with respect to their mutual interreaction by neutrons which they emanate. This phenomenon limits the proximity of the fuel elements to each other for safe storage since neutronic interaction increases when the distance between the fissile fuel elements is reduced. Closer and more economical storage has been achieved by the introduction of a neutron absorbing (or capturing) shield in the cell assemblage.
Elements of spent fuel assemblies freshly removed from a reactor are highly radioactive and therefore they are usually stored vertically submerged in water. The water may contain a dissolved neutron shielding substance. The water also serves to dissipate the heat resulting from the decay of the radioactive matter. Racks for high density storage of fuel elements are commonly of cellular construction with the neutron shield placed between the cells in the form of a solid sheet. The cells are usually long vertical square tubes which are open at the top and through which the fuel elements are inserted. The cells are sometimes with double walls that encapsulate the neutron shield sheets to protect the neutron shield from corrosion or other deterioration resulting from contact with water.
The racks proposed heretofore suffer from disadvantages in that they lack economy and ease of construction. The present invention is a solution to that problem.